Wow this is very decent for a first map, although the usual stuff like skybox and lighting can be fixed, I think the textures needs work. Obviously some of them are custom, so they don't fit with some of the default textures you're placing them with.

Always make sure that your textures are aligned properly otherwise you might end up with odd things like that.

Another thing to work on is the lighting as mentioned earlier. You should make them less bright and put them a bit further away from the walls so you don't get these pure white circles on the walls. Putting a weak regular light combined with a bit brigther light spot with a wide angle often makes the best looking lamps. Put a nice sprite on top of them to make them look even better. Here's a pretty good tutorial on how to make really good looking lighting. http://www.interlopers.net/tutorials/17779

All in all this is really good for being a first map, Especially since making a roleplaying map is pretty hard. Lot's of things to think about. Your level design is quite good.

Edited:
Another pretty simple thing to change would be to change the roofs on the small houses a bit. Right now they are really pointy like > and they don't really look like that in real life. Just add a tiny brush under them so they get a nicer ending and maybe give it another texture to make it look like another material.

For a first map, this is great. You understand lighting and brushwork well.

Give the sun more emotion, right now it's just pure white-looking. Tinting it a natural colour can help bend the atmosphere to a great result. Perhaps make it sunset, or night?

The big red building has misaligned textures; look at where the building ends, there's half of a window.

You're swapping between HL2 and TF2 textures, it looks. They are both very different in terms of art style and can really kill the immersion in a map. Try looking for stock HL2 alternatives, or finding custom textures.

The hotel room (if that's what it is) is too block coloured, due to the TF2 textures. Add some props or decals to break up the repetitiveness. Use them wherever a texture is repeated a lot, to make it more natural-looking.

Make the grass outside displacements, and paint alpha onto it, so it's not just solid grass everywhere. Also add mild noise and bumps to make it more believable.

The subway has yellow light sources, but the light itself is purely white. Try to avoid making all your lights white by changing the hue to that of a more believable colour, and try to match the light source's tone. Avoid making your lights too saturated, though.

Where the map ends, and the skybox starts, the map just cuts off. Either expand the map past the playable area, or create a 3D skybox. For a 3D skybox, use this tutorial, it'll make your maps look like they have a world outside of the playable boundaries, rather than just an area in the middle of nowhere.

The road textures aren't aligned right, move the white lines so they're in the center, like so:

Overall, for a first map, this is very good, and it's a relief to see someone who actually spends time making their first maps before releasing it. If you follow my advice, this map will shape up really nicely, and will look much better.

Always make sure that your textures are aligned properly otherwise you might end up with odd things like that.

Another thing to work on is the lighting as mentioned earlier. You should make them less bright and put them a bit further away from the walls so you don't get these pure white circles on the walls. Putting a weak regular light combined with a bit brigther light spot with a wide angle often makes the best looking lamps. Put a nice sprite on top of them to make them look even better. Here's a pretty good tutorial on how to make really good looking lighting. http://www.interlopers.net/tutorials/17779

All in all this is really good for being a first map, Especially since making a roleplaying map is pretty hard. Lot's of things to think about. Your level design is quite good.

Edited:
Another pretty simple thing to change would be to change the roofs on the small houses a bit. Right now they are really pointy like > and they don't really look like that in real life. Just add a tiny brush under them so they get a nicer ending and maybe give it another texture to make it look like another material.